A concave lens of focal length 20 cm placed in contact with a plane mirror acts as aA. convex mirror of focal length 10 cmB. concave mirror of focal length 40 cmC. concave mirror of focal length 60 cmD. concave mirror of focal length 10 cm

A concave lens of focal length 20 cm placed in contact with a plane mi

1.	A concave lens of focal length 20 cm placed in contact with a plane mirror acts as aA. convex mirror of focal length 10 cmB. concave mirror of focal length 40 cmC. concave mirror of focal length 60 cmD. concave mirror of focal length 10 cm
Answer» Correct Answer - A (a) Power, `P=2P_(L)+P_(M)` or `-1/F=2(-1/0.2)+0orF= 10cm` On silvering the surface of the lens, it behaves as a mirror. Therefore, the combination behaves as a convex mirror of focal length 10 cm.

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